This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-229906 (corresponding to Japanese Unexamined Patent Publication No. 2002-48031) filed on Jul. 28, 2000 and Japanese Patent Application No. 2002-271626 filed on Sep. 18, 2002.
1. Field of the Invention
The present invention relates to an electromagnetic fuel injection device of an internal combustion engine (hereinafter simply referred to as an engine).
2. Description of Related Art
In an electromagnetic fuel injection device, it is desirable to control a fuel injection amount in such a manner that the fuel injection amount is proportioned to a length of a corresponding pulse signal applied, for example, from an engine control unit to a coil (or coil winding). To achieve this, fuel injection characteristics of the fuel injection device need to be approximated to a waveform of the pulse signal applied to the coil. That is, a valve opening period of the fuel injection device at time of energization of the coil needs to be reduced, and a valve closing period of the fuel injection device at time of deenergization of the coil needs to be reduced.
When a magnetic attractive force for attracting a movable core, which reciprocates together with a valve member, toward a stationary core is increased, a valve opening speed is increased to reduce the valve opening period. However, when a number of turns of the coil is increased to increase the magnetic attractive force, a size of the fuel injection device is disadvantageously increased.
Furthermore, when a load of a spring, which urges the valve member toward a valve opening direction, is increased, a valve closing speed is also increased to decrease the valve closing period. However, when the spring load is increased, a valve opening speed of the movable core, which is attracted toward the stationary core against the spring load, and thus of the valve member is disadvantageously reduced.
To address the above disadvantages, in a fuel injection device disclosed in Japanese unexamined patent publication No. 11-148437, positions of a movable core, a stationary core and a coil are adjusted to increase a magnetic attractive force, thereby increasing a valve opening speed to reduce a valve opening period without increasing a number of turns of the coil and without increasing a size of a fuel injection valve.
However, when the magnetic attractive force is increased, a time period required for reducing the magnetic attractive force at time of deenergization of the coil is increased. That is, a valve closing period is increased. As described above, an increase in a spring load causes an increase in a valve closing speed to reduce a valve closing period. However, as described above, when the spring load is increased, the magnetic attractive force for attracting the movable core against the spring load needs to be increased. A portion of the magnetic attractive force, which is increased by adjusting positions of the movable core, the stationary core and the coil, is used to compensate an increase in the spring load, so that it is difficult to increase a valve opening speed.
When the valve opening period or the valve closing period is increased, characteristics of the fuel injection rate become non-proportional to the drive signal applied to the coil (e.g., the signal width of the pulse signal), resulting in variations in the fuel injection amount. Thus, it is difficult to control the fuel injection amount. Particularly, when the signal width of the drive signal applied to the coil is relatively small, for example, during idle operation of the engine, it is difficult to control the fuel injection amount. Thus, in order to provide a required fuel injection amount, the signal width of the corresponding drive signal is increased to inject an excessive amount of fuel. As a result, a fuel consumption is increased, and an amount of noxious components in the exhaust gases increase.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a compact fuel injection device, which achieves a reduced valve opening period and a reduced valve closing period to more precisely control a fuel injection amount.
To address the objective of the present invention, there is provided a fuel injection device including a cylindrical member, a valve body, a valve member, a movable core, a stationary core, an urging means and a coil. The cylindrical member includes a first magnetic portion, a magnetic shield portion and a second magnetic portion arranged in this order from a downstream end of the cylindrical member toward an upstream end of the cylindrical member. The valve body is held by the first magnetic portion of the cylindrical member and includes at least one fuel injection hole and a vale seat arranged on an upstream side of the injection hole. The valve member is reciprocably received in the cylindrical member and includes an abutting portion. The abutting portion is seatable on the valve seat to close the injection hole and is also liftable from the valve seat to release the injection hole. The movable core is arranged on an upstream side of the valve member and is reciprocable together with the valve member. The stationary core is arranged on an upstream side of the movable core and is opposed to the movable core in the cylindrical member. The urging means is for urging the valve member against the valve seat. The coil is arranged radially outward of the cylindrical member to generate a magnetic force for attracting the movable core toward the stationary core upon energization of the coil. The cylindrical member, the stationary core and the coil are sized to satisfy the following conditions: 5 mmxe2x89xa6Laxe2x89xa610 mm, 0 mmxe2x89xa6Lbxe2x89xa61.0 mm, Lb less than Lc, and 0.5xe2x89xa6Ld/La xe2x89xa61.5, wherein La is the axial length of the coil, Lb is the axial distance between a downstream end surface of the coil and a downstream end surface of the magnetic shield portion, Lc is the axial distance between the downstream end surface of the coil and a downstream end surface of the stationary core, and Ld is the axial length of the magnetic shield portion.
To achieve the objective of the present invention, there is also provided a fuel injection device including a body, a cylindrical stationary portion, a valve member, a movable portion, an urging means and a coil. The body includes at least one fuel injection hole and a valve seat arranged on an upstream side of the injection hole. The cylindrical stationary portion exhibits magnetism and is secured to the body. The stationary portion includes a main portion and a reduced size portion, which are arranged in an axial direction of the stationary portion. A cross-sectional area of the reduced size portion measured in a plane perpendicular to an axis of the stationary portion is smaller than a cross sectional area of the main portion measured in a plane perpendicular to the axis of the stationary portion. The valve member is reciprocably received in the body and includes an abutting portion. The abutting portion is seatable on the valve seat to close the injection hole and is also liftable from the valve seat to release the injection hole. The movable portion is arranged on a downstream side of the stationary portion and also on an upstream side of the valve member and is reciprocable together with the valve member. The urging means is for urging the valve member against the valve seat. The coil is coaxial with the stationary portion and is arranged radially outward of the stationary portion to generate a magnetic force for attracting the movable portion toward the stationary portion upon energization of the coil. The stationary portion is sized to satisfy the following condition: 0.2xe2x89xa6Sb/Saxe2x89xa60.9, wherein Sa is the cross-sectional area of the main portion, and Sb is the cross-sectional area of the reduced size portion. The stationary portion and the coil are sized to satisfy the following condition: 0.1xe2x89xa6(Lf+Lc)/Laxe2x89xa61.0, wherein La is the axial length of the coil, Lf is the axial length of the reduced size portion, and Lc is the axial distance between a downstream end surface of the coil and a downstream end surface of the stationary portion.